Method of magnetic resonance imaging

Abstract

In a magnetic resonance imagining method, using an effect that a fluid flows out of a plane where it is selectively excited between the time of applying a 90° radio frequency pulse and the time of applying of a 180° radio frequency pulse, two, images are separately constructed from multiple echo signals which are sampled before applying the 180° radio frequency pulse and multiple echo signals which are sampled after applying the 180° radio frequency pulse. An image of the fluid flow and an image of a static part are separated from each other based on a difference between the two constructed images.

What is claimed is: 
     
       1. A method of magnetic resonance imaging comprising the sequential steps of: (a) selectively exciting a region of interest to be imaged by applying to the region of interest a first radio frequency pulse and a gradient magnetic field having a gradient in a first direction, the region of interest including a fluid part and a static part;   (b) applying to the region of interest a readout gradient magnetic field having a gradient in a second direction perpendicular to the first direction while periodically inverting a polarity of the readout gradient magnetic fields, and   an encode gradient magnetic field having a gradient in a third direction perpendicular to both the first direction and the second direction;     (c) measuring first multiple echo signals generated by the region of interest during the step (b);   (d) selectively exciting said region of interest by applying to the region of interest a second radio frequency pulse and the gradient magnetic field having a gradient in the first direction;   (e) applying to the region of interest the readout gradient magnetic field having a gradient in the second direction while periodically inverting the polarity of the readout gradient magnetic fields, and   the encode gradient magnetic field having a gradient in the third direction;     (f) measuring second multiple echo signals generated by the region of interest during the step (e);   (g) constructing a first image of the region of interest on the basis of the measured first multiple echo signals, and   a second image of the region of interest on the basis of the measured second multiple echo signals; and     (h) obtaining an image of only the fluid part of the region of interest on the basis of a difference between the first image and the second image.   
     
     
       2. A method of magnetic resonance imaging according to claim 1, wherein a frequency space to be measured is divided into a plurality of regions; wherein said first and second multiple echo signals are measured repeatedly in each of the regions; and   wherein said first and second images are constructed on the basis of said first and second multiple echo signals measured repeatedly in each of the regions.   
     
     
       3. A method of magnetic resonance imaging according to claim 1, wherein said readout gradient magnetic field has a sine waveform. 
     
     
       4. A method of magnetic resonance imaging according to claim 3, wherein a frequency space to be measured is divided into two halves; wherein the first multiple echo signals and the second multiple echo signals are measured in only one of the two halves of the frequency space; and   wherein the first image and the second image are constructed only on the basis of the first multiple echo signals and the second multiple echo signals measured in only one of the two halves of the frequency space.   
     
     
       5. A method of magnetic resonance imaging according to claim 1, wherein a frequency space to be measured is divided into two halves; wherein the first multiple echo signals and the second multiple echo signals are measured in only one of the two halves of the frequency space; and   wherein the first image and the second image are constructed only on the basis of the first multiple echo signals and the second multiple echo signals measured in only one of the two halves of the frequency space.   
     
     
       6. A method of magnetic resonance imaging according to claim 1, wherein a frequency space to be measured is divided into two halves, and only one of the two halves is divided into a plurality of regions; wherein the first multiple echo signals and the second multiple echo signals are measured repeatedly in each of the regions; and   wherein the first image and the second image are constructed only on the basis of the first multiple echo signals and the second multiple echo signals measured repeatedly in each of the regions.   
     
     
       7. A method of magnetic resonance imaging according to claim 1, wherein the image of the fluid part of the region of interest represents fluid flowing through a slice of the region of interest, the slice being perpendicular to the first direction. 
     
     
       8. A method of magnetic resonance imaging according to claim 1, wherein the step (h) includes compensating for signal decay due to transverse relaxation occurring between measurement of the first multiple echo signals in the step (c) and measurement of the second multiple echo signals in the step (f).